A large number of semiconductor devices are typically fabricated on a common semiconductor wafer having a diameter up to 12 inches or more and then are separated (i.e. singulated) for packaging as individual devices. These semiconductor devices, which can be integrated circuits (ICs), microprocessors, microelectromechanical systems (MEMS), microfluidic devices, sensors, etc., are conventionally singulated by saw cutting. The use of saw cutting requires a spacing (i.e. a street) between adjacent devices which are being singulated with this spacing being up to 100 microns or more wide; and this spacing limits the number of devices which can be fabricated from the semiconductor wafer. Additionally, saw cutting generates debris which can contaminate the devices or become lodged in moveable members of MEMS devices or in fluid channels of microfluidic devices. Furthermore, saw cutting must be performed along straight lines in a serial fashion one cut at a time; and this limits the shape of the devices to being square or rectangular and generally all of the same size. Saw cutting is also time consuming since each saw cut must be carefully aligned with each street separating adjacent rows of devices to prevent damage to the devices. For all of the above reasons, conventional saw cutting is disadvantageous so that an advance in the art is needed to improve the singulation of devices from semiconductor wafers.
The present invention provides such an improvement in the art by providing a method for singulating one or more die from a semiconductor wafer (i.e. a substrate) which relies on etching one or more trenches into the wafer from a backside thereof opposite a device side of the wafer. A handle wafer is then attached to the backside of the semiconductor wafer according to the present invention; and then a sacrificial layer (e.g. comprising silicon dioxide or a silicate glass) on the device side of the wafer is partially or completely etched away to finish the singulation process and to release any microelectromechanical systems (MEMS) devices which may be present on the die. A retainer, which is generally formed from a device layer (e.g. comprising monocrystalline silicon or polycrystalline silicon) on the device side of the substrate, is anchored to a portion of the semiconductor wafer outside of the die being singulated to form a frame about the die after singulation thereof, thereby retaining the die in place for further processing, movement, storage, transporting, etc., of the die.
The present invention is compatible with standard semiconductor processes and allows all of the die on the wafer to be singulated simultaneously in a parallel process. This saves time and cost and also increases yield and performance by minimizing die handling and particulates which would otherwise occur if conventional sawing were used to singulate the die. Additionally, by retaining the die in place after singulation between the frame and the handle wafer, post-processing of the die can be performed, for example, to deposit a metal onto the die, or to add a wear-resistant material, an adhesion-reducing material, a stiction-reducing material, or a passivation material onto the die. Once the frame is lifted off of the handle wafer, all of the die can remain in place in a spaced-apart arrangement on the handle wafer so that they can be individually picked up and permanently packaged (e.g. in a dual in-line package or in a pin grid array package). A package can also be formed for the singulated die according to the present invention by leaving the frame temporarily fastened to the handle wafer using a clamp or a clip.
These and other advantages of the present invention will become evident to those skilled in the art.